Types

Records hold named fields, newline-separated. Sum types hold case variants. A field or a variant payload can carry its own refinement.

public type Phase {
    case red
    case green
    case yellow(seconds_remaining: i32
        where seconds_remaining >= 0)
}

public type IntStack {
    capacity: usize
    len: usize where len <= capacity
    data: [i64] where data.len() == capacity
}

Construction qualifies the variant (Phase.red); inside a match the dot-prefixed form is the pattern. A type that refers to itself goes through Box(T). There is no null; an absent value is Option(T).